This invention relates to rigging for sailing vessels and more particularly to a boom and the attachment between the boom and an upright support structure such as a mast.
In conventional sailing vessels having a mast, a boom is employed to support the lower edge of the mainsail. The boom, usually constructed of extruded aluminum, is connected at one end of the mast by a swivel or gooseneck fitting. The clew of the mainsail is supported at the other end of the boom, usually in an adjustable manner, using an outhaul. The leading edge of the mainsail, or luff, is supported in a slot or track extending lengthwise on the mast, with the tack being secured to the boom.
By necessity, numerous controls are employed to control the position of the boom, which is swingable approximately 180 degrees behind the mast, and the free end is tiltable upwardly. Conventionally, a traveler is mounted across the boat near the free end of the boom, and a mainsheet system is connected between the traveler and the boom. This system serves to control the extent of outward movement of the boom and also serves to hold the end of the boom down, as long as the attachment point of the mainsheet at the deck is beneath the attachment point on the boom. The traveler allows the lower attachment point to move back and forth athwartships to extend the range of downward force of the mainsheet.
At certain points of sailing, such as during reaching or running, the boom extends beyond the end or extent of control of the traveler, and a separate control, known as a boom vang, is employed to restrain upward movement of the end of the boom. The vang usually extends between the base of the mast and a location about one quarter of the length of the boom behind the gooseneck. The vang is employed as a tension member and is typically constructed from wire, rope, or telescoping rods or pipes, which may include a piston operation.
Finally, a topping lift must be employed to prevent downward sag of the free end of the boom when the sail is lowered. The topping lift is typically between the top of the mast and the end of the boom.
In addition, the boom may be provided with an elongated cylindrical cavity to enable furling or reefing of the mainsail into the boom. For example, the foot of the mainsail may be attached to an elongated shaft or tube extending the length of the cavity. The tube may be rotated to roller reef or furl the sail from the foot as the halyard is released. In most applications the angle maintained between the boom and mast is highly critical in order to allow the sail to roll up evenly. Even a slight deviation from the critical angle may cause bunching of the sail at one end and jamming of the system.
Since the mainsail is triangular, the furling operation requires that a greater quantity of sail material must be accommodated in the forward portion of the boom. If a conventional single extrusion is used to make the boom, this may require the boom to have a cross section which is excessively large, heavy and bulky.